Function emit_write 

pub fn emit_write(
    w: &mut CodeWriter,
    access: &str,
    ty: &ResolvedType,
    enc: &FieldEncoding,
    registry: &TypeRegistry,
    field_name: &str,
)

Emit code to write a field to w: &mut BitWriter.

access is the Rust expression for the value (e.g. self.name or &self.data). For Encoding::Delta, this function is a no-op (the delta module handles it).